As emphasis is being placed on simple and intuitive user interfaces, many new techniques for interacting with electronics devices are being developed. Touch-screen interfaces are becoming popular because of their ease of use. By touching a touch-screen display or touch panel using fingers or stylus, a user can make selections or move cursors, etc.
Among the various types of touch technologies, capacitive-touch sensing is gaining popularity because of its reliability, ease of implementation and capability to handle multi-touch inputs. Capacitive-touch sensing can be accomplished by either detecting a change in self-capacitance or a change in mutual capacitance. A change in mutual capacitance enables multi-touch events to be detected. Consequently, all of the latest capacitive touch panels detect changes in mutual capacitance for touch sensing.
Mutual capacitance based touch panels can have different patterns of sensor electrodes. One of the most common electrode patterns is called a diamond pattern in which both horizontal electrodes and vertical electrodes are overlaid on each other to cover an entire display region. The nodes at intersections between the horizontal and vertical electrodes form the mutual capacitance. In the presence of an external conducting object, mutual capacitance value decreases from a normal or ambient value. The amount of change in mutual capacitance is different at different nodes of the diamond pattern for an external conducting object. Determining the exact shape of a touching object would seem to be intuitive by using a threshold-based method to isolate the region of touch. Nevertheless, intuitive threshold-based methods do not adequately work due to many reasons like the coarseness of the grid of electrodes and various ambient noise sources.
In case of handheld devices, power consumption is an important criterion to be considered when designing the device. The power consumption of the device increases significantly as the number of electrodes increases. Consequently, there is a practical limitation to the density of electrodes of a touch panel. The typical pitch between electrodes is 4-5 mm. Given a 5×2.7 inch display, only a 30×17 grid of electrodes at 4 mm pitch can be realized. The size of a touching object could be as small as 2×2 mm. Thus, it is possible to contain the shape of the entire touching object inside four grid nodes. In this case, however, the mutual capacitance of only a few electrodes is affected, and sensing the touching object would be based on low-resolution data. Even in the case of a larger touching object, determining the orientation of the touching object would be performed based on low-resolution data.
Secondly, many unavoidable ambient noise sources exist that affect quality of the mutual capacitance data. For example, in order to reduce the display panel thickness, the touch sensors are placed very near to the display driving lines. This technology is referred to as on-cell capacitive sensing. In on-cell capacitive touch panels, the display noise in touch signals due to the cross-coupling between display lines and touch sensors is a critical problem. Though some noise removal techniques are being proposed, it is impossible to completely eliminate such noise. Additionally, there are many other noise sources, like charger noise, environmental changes, etc., that affect the quality of the mutual capacitance data.
In view of the foregoing, estimating the shape and orientation of the touching object in a low-resolution touch grid in the presence of noise is a challenge, particularly for high-end applications like games, paintings, etc.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent upon a reading of the specification and a study of the drawings.